1. Field of the Invention
The present invention relates to machinery used to test containers for wafer cassettes and, more particularly, relates to a hoist jig that repeatedly cycles two wafer containers, such as front opening unified pods, in order to simulate the vertical forces exerted by a selected overhead transport system.
2. Description of the Related Art
In the manufacturing process of semiconductor wafers, different-sized wafers require cassettes having different dimensions. Many current production lines use 150 mm and 200 mm diameter wafer; next generation lines will use 300 mm wafers. Therefore, next generation equipment has been designed to accommodate 300 mm wafers. One type of such equipment is wafer-storage cassettes.
Wafer transfer systems are used to provide an automated transfer of semiconductor wafers from one position to another position. For example, the wafers contained in a cassette may be moved individually to a processing chamber for depositing and patterning layers of material for forming integrated circuit chips. Robotic handling devices are preferred, since human handling is more likely to cause contamination.
The wafer-storage cassettes are often themselves stored and transferred in a pod. One type of wafer storage pod is referred to as a Standardized Mechanical InterFace (SMIF) pod. A SMIF pod is described in U.S. Pat. No. 5,653,565, which is assigned to Bonora et al. and is incorporated by reference herein in its entirety. The SMIF pod includes a cover that mates with a door to provide a sealed environment for the wafers within the cassette. When the wafers are to be transferred to a processing station, the pod is placed onto an access port of a transfer system such that the pod door is in contact with the access port.
Another type of wafer storage pod is sometimes referred to in the industry as a Front Opening Unified Pod (FOUP). A FOUP has an access door located on a side that is perpendicular to horizontally stored wafers and is used for 300 mm diameter semiconductor wafers. Automated transfer systems for use with FOUPs have been designed. FOUPs are designed to be lifted and lowered by automated material handling systems (AMHS), such as overhead hoist transport (OHT) systems. OHT systems result in mechanical wear of the FOUP due to repeated lifting and lowering.
A hoist jig comprises a vertically upright center member having a first surface and a second surface and a base coupled to the center member. The hoist jig further comprises a first support arm and a second support arm. The first support arm is coupled in a vertically slideable relationship to the first surface of the center member, the first support arm being configured to receive a first wafer storage container. The second support arm is coupled in a vertically slideable relationship to the second surface of the center member, the second support arm being configured to receive a second wafer storage container. The hoist jig further comprises a cycle mechanism that is operable to cycle the first wafer storage container and the second wafer storage container in a vertical up-and-down motion. The cycle mechanism is further operable to maintain the first wafer storage container and the second wafer storage container in a counterbalanced relationship with each other.
A method of testing two wafer containers simultaneously comprises coupling a first wafer container to a first support arm, wherein the first support arm is coupled to a first surface of a center member. The method further comprises coupling a second wafer container to a second support arm, wherein the second support arm is coupled to a second surface of a center member. The method further comprises maintaining the first wafer container and the second wafer container in a counterbalanced relationship with each other. The method further comprises cycling the first wafer container and the second wafer container in a vertical up-and-down motion at a speed that simulates the vertical forces exerted by a selected automated material handling system.